“All I have learned, I learned from books.”
– Abraham Lincoln
And you learn even more by writing books than reading them. If you want to learn a subject thoroughly, write a book about it. Even if you are writing fiction, you will still learn a great deal about the world and human nature if you do your research properly.
The Sibling Writery 
I find that I learn more about operas and songs when I write blog posts because I want to make them interesting to share and am learning to pick out the most important details, I still have lots of improvements to make in my writing but this is a good exercise.